Maths for A Level Biology - updated edition

Chapter 1 Processed numbers In Biology, you will often have numbers that need to be processed so that you can make biological sense of them. This section will show you how to decode the question asked so that you can make the correct calculation. It is generally the use of language, rather than the maths, that is the problem. 2.1 Percentage One very common operation is ϐinding a percentage, but students often fail to make the appropriate calculation because they have not understood what is being asked. 2.1.1 Per cent calculation ‘Per cent’ means ‘by 100’ so when you calculate a per cent, it is as if you were ϐinding the number out of 100. When faced with a problem, if you’re not sure how to proceed, give yourself an easy example ϐirst so you can see what to do. Supposing you are asked to ϐind the percentage of black-tailed godwits in their summer plumage, given that 288 of these birds have their summer colours, out of a total population of 720. You may not even have heard of godwits, but you do not need to know that these are wading birds found in wet meadows and grassy marshes, to work out the answer. First, make up a calculation based on easy numbers. Pretend that 3 out of a population of 6 have their summer coloration. You know intuitively, that 3 out of 6 is 50% because you know that 3 is half of 6. Now rearrange the numbers 3, 6 and 100 to make an equation that gives you 50% as your answer. Because these numbers are easy, you can see 3 6 × 100 = 50%. So this is how you work out the problem. Substitute the numbers given to you to ϐind the answer: Percentage with summer plumage = number with summer plumage total number × 100 = 288 720 × 100 = 40.0% 2 QUICKFIRE 2.1 North Korean scientists say that they have produced two cloned wolves from the 251 embryos that they implanted into surrogate mothers. What was their percentage success? Pointer % = number given total number × 100 A godwit Mathematics for Biology 32